P0641 code

2003 LB7. 127K miles. Saturday I noticed a slight irregular idle during a 4-5 minute idle. This morning when I started it for work, the check engine light stayed on, but it seemed to run normally. Same when I left work.

Got home, shut it off and went into the garage to get my scan tool. Connected the tool and saw the P0641 (sensor reference voltage A circuit / open) code (key on engine off). Cleared the code and it immediately came back along with the "reduced power" message in the DIC. Tried starting and it would barely stay running. At this point I also saw a P0193, but it didn't store that code. Shut it off and went in the house to call a friend and do some research. Went out a little later and it started back up with just an occasional bounce in the idle.

We watched on the scanner and could see the fuel pressure bounce wildly when the idle changed. My buddy (who works mostly on Ford diesels) seems to think it's the fuel pressure sensor failing.

I just wanted to see what everyone here thinks before I buy a new FPS.

Bob
tufcj

Change the fuel filter, first.

I'll add that the fuel pressure sensors seldom fail, but the regulators do.

Fuel filter was replaced about 2000 miles ago, at the last oil change. Hasn't been a problem. I used a Luber-Finer fuel filter.

Would the regulator cause a P0641? We watched the fuel pressure on the scanner vary at idle from 4700PSI to 18,000psi, the idle would bounce with the pressure changes.

Thanks.

Bob

if the idle is oscillating with the pressure changes there is a good chance that the pressure is actually doing what you are seeing and the regulator is getting flaky. I'd start with teh common failure regulator and see what happens from there.